1. Field of the Invention
The present invention relates to a magnetoresistance effect element for reading the magnetic field intensity of a magnetic recording medium or the like as a signal and, in particular, to a magnetoresistance effect element which is capable of reading a small magnetic field change as a greater electrical resistance change signal, and further relates to a magnetoresistance device, such as a magnetoresistance effect type head, using such a magnetoresistance effect element.
2. Description of the Prior Art
Following the recent increase in density of magnetic recording, induction type magnetic heads are being replaced by magnetoresistance effect type heads (hereinafter referred to as "MR heads") in the field of read-only heads. The MR head utilizes a magnetoresistance effect and senses a change in magnetic flux from a recording medium, that is, a signal magnetic field, based on a change in resistance. An output voltage is given by the product of a change in resistance of a magnetoresistance effect element (hereinafter referred to as "MR element") sensing a change in magnetic flux and a sense current flowing in the MR element. Accordingly, the output voltage can be set large, and further, a value of the output voltage can be freely changed by a value of the sense current. Thus, as different from the induction type magnetic head, the output voltage does not depend a relative speed between a head sensor portion and the recording medium.
In the MR head, the MR element which senses the change in magnetic flux from the recording medium to change its resistance is made of an NiFe alloy. The NiFe alloy is excellent in anisotropy magnetoresistance effect (hereinafter referred to as "AMR") and, since it is a soft magnetic material, its response is excellent in a small magnetic field.
However, for the NiFe alloy to perform the optimum operation as an MR element, two biases are required. Specifically, as the first bias, a lateral bias is required which is applied to a surface of the magnetic recording medium in perpendicular thereto and to a surface of the MR element in parallel thereto for achieving the linearity of a magnetic field response of the MR element. The lateral bias is generated by the flow of sense current in a soft film bias layer (made of, for example, NiFeRh or NiFeCr) adhered to an NiFe alloy layer via a magnetic separation layer (made of, for example, Ta).
As the second bias, a longitudinal bias is required for suppressing Barkhausen jump noise (hereinafter referred to as "BHN") which is caused upon movement of domain walls of multidomains in the MR element in response to the magnetic field. The longitudinal bias is given by an exchange coupling magnetic field (hereinafter referred to as "Hua") caused by a laminate film of the NiFe alloy and an antiferromagnetic material (for example, FeMn) as the MR element. The Hua is a magnetic field generated by an exchange interaction at a contact surface between the ferromagnetic material and the antiferromagnetic material.
By this exchange coupling, the longitudinal bias is applied to the NiFe alloy being the MR element. As a result, a domain structure of the NiFe alloy approximates a single domain to control BHN.
In the MR using the AMR, since the MR element is the NiFe alloy, a magnetoresistance change ratio (hereinafter referred to as "MR change ratio") is about 2 to 3%. Therefore, recently, as a film replacing NiFe, attention has been paid to artificial lattices and spin valve films (for example, PHYSICAL REVIEW B volume 43, page 1297, in 1991, and Japanese First (unexamined) Patent Publication No. 4-358310) revealing a giant magnetoresistance effect (hereinafter referred to as "GMR"). Among the films revealing the GMR, since the spin valve film is simple in structure and small in operation magnetic field as compared with the artificial lattice, attention has been further paid thereto. An example of actual review of the spin valve film for use in the magnetoresistance effect element of the magnetoresistance effect type reproduction head is reported in IEEE TRANSACTION ON MAGNETICS volume 30, page 3801, in 1994. The reported spin valve film is a magnetic multilayered film which is formed by coupling a soft magnetic layer (also called a free layer and made of NiFe or the like) responsive to a magnetic field, and a fixed layer in the form of a two-layer film of a ferromagnetic layer (NiFe, CoFe, CoFeNi or the like) and an antiferromagnetic layer (FeMn), via a non-magnetic material (Cu, Au, Ag or the like) interposed therebetween. The spin valve film shows a very high MR change ratio of 3 to 10% as compared with the NiFe alloy. According to the GMR of the spin valve film, the resistance thereof becomes minimum when magnetization (Mf) of the soft magnetic layer which can freely respond to the magnetic field and magnetization (Mp) of the fixed layer (two-layer film whose magnetization direction is fixed due to Hua generated at a contact surface between the ferromagnetic layer and the antiferromagnetic layer) are parallel to each other. It is assumed that the resistance at this time is R.sub.0. On the other hand, when Mf and Mp are antiparallel to each other, the resistance of the spin valve film becomes maximum. It is assumed that the resistance at this time is R.sub.m. The GMR change ratio is given by (R.sub.m -R.sub.0)/R.sub.0.
When the directions of magnetization of those layers are parallel to each other, the current flowing in the spin valve film is not subjected to scattering of electrons due to spins at the interface between the non-magnetic layer and the soft magnetic layer and at the interface between the non-magnetic layer and the fixed layer so that the resistance becomes minimum.
On the other hand, when the magnetization directions are antiparallel to each other, the current flowing in the spin valve film is subjected to scattering of electrons due to spins at the interface between the non-magnetic layer and the soft magnetic layer and at the interface between the non-magnetic layer and the fixed layer so that the resistance becomes maximum.
In the MR head using the AMR and the spin valve head (MR head) using the GMR, a so-called pinning operation is required which generates Hua by stacking and joining the ferromagnetic film and the antiferromagnetic film. In the MR head using the AMR, the pinning is carried out for generating a longitudinal bias magnetic field to control the BHN. In the spin valve head, the pinning is carried out for fixing the magnetization.
As materials for the antiferromagnetic films which generate Hua, .gamma.-FeMn alloy (for example, U.S. Pat. No. 4,103,315), NiO, .alpha.-Fe.sub.2 O.sub.3 and Mn gamma alloy containing an element selected from Fe, Co, Cu, Ge, Ni, Pt and Rh (Japanese Second (examined) Patent Publication No. 60-32330) have been known. Further, U.S. Pat. No. 4,755,897 has proposed FeMn added with Cr.
However, the foregoing materials of the antiferromagnetic films are not sufficient in corrosion resistance or thermal stability, resulting in deterioration of Hua due to corrosion or deterioration of Hua due to temperature change. In addition to the foregoing problem, a high blocking temperature (at which Hua becomes zero) is required in the spin valve film. Further, during a fabricating process, it is required that the blocking temperature is within a certain range for performing an orthogonalization heat treatment and that the blocking temperature can be selected to some extent.